Process for collecting metal whiskers



March 29, 1966 c, MQRELQCK ETAL 3,243,284

PROCESS FOR COLLECTING METAL WHISKERS Filed Nov. 22, 1965 13 To Vacuum /n vemors Char/es R More/00k,-

Fred 5. Lubo sky,

7' h e/r Attorney United States Patent 3,243,284 PROCESS FOR COLLECTING METAL WHISKERS Charles R. Morelock, Ballston Spa, and Fred E. Luborsky,

Schenectady, N.Y., assignors to General Electric Company, a corporation of New York Filed Nov. 22, 1963, Ser. No. 325,645 2 Claims. (Cl. 75-81) This invention relates to the production of sub-micron size metal whiskers and more particularly to an improved method for collecting sub-micron sized metal whiskers from their growth substrate.

The production of metal whiskers grown by vapor phase deposition has become increasingly important, since such whiskers are of value as reinforcing agents in making high strength composites, for example. Additionally, whiskers produced of magnetic materials notably iron, nickel, cobalt and alloys of these metals with each other, are of great value in producing magnets having greater coercive forces than previously attainable. However, since the whiskers are of extremely small sizes, generally less than one micron, particularly when intended for magnetic use, difficulty is encountered in removing them from the substrate on which they are grown and in collecting them for subsequent processing.

It is therefore the principal object of this invention to provide an improved process for removing sub-micron size metal whiskers from their growth substrate and collecting them for processing.

Other objects and advantages of this invention will be in part obvious and in part explained by reference to the accompanying specification and drawings in which:

FIG. 1 is a schematic illustrating the manner in which whiskers are removed from their growth substrate in a bath of mercury;

FIG. 2 is a schematic illustrating the manner in which the whiskers are removed from the mercury into a liquid non-reactive with the whiskers; and

FIG. 3 is a schematic illustrating one method for removing the whiskers from the non-reactive liquid.

Generally, the process of this invention comprises immersing a growth substrate which has the metal whiskers attached thereto in mercury, vibrating the substrate, or otherwise providing for relative motion between the substrate and the mercury, to free the whiskers therefrom, adding a liquid to the mercury which is non-reactive with respect to the whiskers and then mixing the added liquid and the mercury to transport the whiskers from the mercury into the added liquid and, finally, filtering the added liquid to remove the whiskers therefrom.

As was indicated earlier, the process of the present invention has particular application with regard to the removal of metal whiskers, and particularly metal whiskers of sub-micron size, from their growth substrate so that they might be collected for further processing and use.

The copending application of Charles R. Morelock, Serial No. 200,023, filed May 31, 1962, and assigned to the same assignee as the present invention, describes a particularly efficacious manner for producing metal whiskers by vapor deposition. This process generally comprises vaporizing a source metal in an enclosed, continuously evacuated chamber and depositing the vaporized metal on a growth substrate which is maintained at carefully controlled temperatures. Gettering is effected simultaneously with evacuation so that the whiskers that are produced are freer of defects than whiskers previously produced by other techniques. The whiskers that are produced by the Morelock process are generally less than one micron in size and are, therefore, comparatively difficult to remove from the substrate from which they have grown. A more complete description of the process can be obtained by referring to the cited copending application.

The present process can be understood best by referring to the accompanying drawing. In FIG. 1, numeral 10 indicates a vessel which contains a quantity of liquid mercury 11. To carry out the process, a growth substrate such as a metal sheet 12 from which whiskers 13 extend, the whiskers being greatly enlarged for purposes of illustration, is immersed in mercury 11. After immersion, the growth substrate 12 is vibrated by a vibrator 15 shown attached to the upper end thereof, so that relative motion is created between the growth substrate 12, the whiskers 13 and the mercury 11. This physical vibration results in an unexpectedly complete freeing of the whiskers from the substrate and their passage into the mercury bath. Obviously, due to the specific gravity of the mercury, the whiskers rise to the surface and es sentially float on the top.

After the whiskers 13 have been freed from substrate 12, the substrate is withdrawn and a quantity of a second liquid 16 (liquid other than mercury) is added. This liquid need only be non-reactive with respect to the whiskers, that is, it should neither combine chemically with the whiskers nor should it contain a component such as oxygen that will cause oxidation thereof. Organic liquids are particularly useful, particularly those such as toluene, benzene and the higher aromatic hydrocarbons which can be removed without leaving any film or residue on the particles. One the other hand, deoxygenated water or water having a small amount of dichromate, for example sodium or potassium dichromate added, can also be effectively used.

After the second liquid 16 is added to the vessel, the combination is mixed, as by means of a mixer 17, so that the whiskers contained in the mercury Will contact the interface between the two liquids and pass into the liquid 16. Agitation or mixing for a reasonable time will ensure essentially complete withdrawal of the whiskers into the lighter of the two liquids. The liquid 16 then containing the whiskers 13 can be poured off or decanted into a filtering vessel 20 which contains a filter member 21 that permits passage of liquid 16 therethrough into the bottom of filter 20. Filter member 21 contains holes 22 through which liquid 16 passes. Obviously, these holes 22 are extremely small, since the particles that are filtered out are less than one micron in size. A filter such as a glazed ceramic filter is outstandingly useful since the surface is very smooth and the particles do not tend toward becoming imbedded. In addition to not becoming imbedded, the whiskers 13 generally become commonly aligned so that where some orientation is desired it can be achieved with less difiiculty.

In the event that magnetic whiskers, that is those composed of iron, nickel, cobalt or alloys of these metals with each other, are being collected, it is possible to effect a relatively complete orientation thereof by subjecting the liquid 16 in the top of filter 20 to an applied magnetic field which has a component passing through the liquid in the direction in which whisker alignment is sought.

Although the present invention has been described in connection with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and the appended claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A method for removing sub-micron size metal Whiskers from their growth substrate and collecting the same comprising, immersing the substrate and attached whisker in mercury, vibrating the substrate while immersed in the mercury to free the whiskers therefrom, removing the substrate from the mercury, adding a quantity of liquid non-reactive with respect to the whiskers and to the mercury and mixing the two together to collect the whiskers in the added liquid, removing the whisker bearing added liquid from the mercury, and filtering the whiskers from the removed liquid.

2. A method as defined in claim 1 wherein the added liquid is an organic hydrocarbon.

References Cited by the Examiner UNITED STATES PATENTS 1,957,819 5/1934 Cowan 7563 4 "2,383,659 8/1945 Lebedeif 75-63 2,531,547 11/1950 Ayres 210 511 2,686,592 8/1954 Miller -5. 209-163 2,923,648 2/1960 KBurg 134--12 2,974,104 3/1961 Paine et a1. 75.5 3,113,018 12/1963 Young 7581 OTHER REFERENCES DAVID L. RECK, Primary Examiner.

15 HYLAND BIZOT, Examiner.

N. F. MARKVA, Assistant Examiner. 

1. A METHOD FOR REMOVING SUB-MICRON SIZE METAL WHISKERS FROM THEIR GROWTH SUBSTRATE AND COLLECTING THE SAME COMPRISING, IMMERSING THE SUBSTRATE AND ATTACHED WHISKER IN MERCURY, VIBRATING THE SUBSTRATE WHILE IMMERSED IN THE MERCURY TO FREE THE WHISKERS THEREFROM, REMOVING THE SUBSTRATE FROM THE MERCURY, ADDING A QUANTITY OF LIQUID NON-REACTIVE WITH RESPECT TO THE WHISKERS AND TO THE MERCURY AND MIXING THE TWO TOGETHER TO COLLECT THE WHISKERS IN THE ADDED LIQUID, REMOVING THE WHISKER BEARING ADDED LIQUID FROM THE MERCURY, AND FILTERING THE WHISKERS FROM THE REMOVED LIQUID. 